Thyroid cancer is the most rapidly rising incident cancer in women and the second most rapidly rising incident cancer in men in the United States. Project 2 will take a clinical and translational genetics approach to identify and characterize genes and their pathways that play a role in the initiation of heritable and sporadic follicular thyroid cancer (FTC) for the translational purposes of the earliest diagnosis. Towards these goals, we will take a 3-pronged approach to examine the earliest events in FTC initiation: germline initiating events in human heritable FTC, somatic initiating events in sporadic FTC and finally physiologic validation and mechanism resolution in a murine model. Specifically, we will utilize germline (inherited) predisposition to reflect the earliest initiating event by utilizing an heritable thyroid neoplasia disorder, Cowden syndrome (CS), which is a difficult-to-recognize, under-diagnosed autosomal dominant disorder characterized by follicular thyroid adenomas (FA), FTC and breast cancer. We plan to prospectively accrue 1,000 probands by set criteria, perform comprehensive PTEN alteration (DMA, RNA and protein) analysis and find the most parsimonious subset of clinical features by logistic regression analysis that will give a fixed likelihood of a PTEN alteration for purposes of referral as well as for purposes of correlating PTEN alteration and features associated with FTC vs FA risk. Second, we will identify and characterize the genes which when differentially expressed differentiate sporadic FTC from FA and independently validate our preliminary data which yielded a 3-gene combination, the latter mandatory before routine clinical application. This will allow the pre-surgical diagnosis of malignancy amongst all follicular thyroid nodules, something which remains extremely challenging on fine needle cytology. Importantly, if validated, our data would allow the pre-surgical diagnosis of FTC versus FA in the clinical arena. The genes which differentiate FTC from FA may play a role in the process of initiating sporadic FTC-genesis. Third, we propose a thyroid specific Ptenconditional knock-out murine model that will allow mechanism resolution for the first 2 aims on human heritable FTC and sporadic FTC initiation.